Conventional cameras offer a variety of features to photographers. One such feature is a mid-roll rewind feature. When the mid-roll rewind feature is selected, a partially exposed photographic filmstrip in the camera is completely wound back into a film cartridge.
A photographer would use the feature when, for example, there was a partially exposed roll of 100 speed film in a camera left over from daytime outdoor picture taking, and now the photographer desired to take pictures outdoors at night with a higher speed film. After the mid-roll rewind is accomplished, the 100 speed film is removed from the camera and replaced with the higher speed film. Photofinishers typically would not create prints from the unexposed frames on the 100 speed film, thereby saving the photographer from paying for worthless images that would be generated if the photographer were forced to take pictures in order to remove the 100 speed film from the camera.
Prior art cameras with a mid-roll rewind feature included a shutter button for commencing a picture taking sequence and a separate mid-roll rewind button for actuating the mid-roll rewind operation. A problem with such prior art cameras is that a separate button or switch is required to actuate (start) the mid-roll rewind mode. A further problem is that a camera operator may accidentally press the mid-roll rewind button, unintentionally causing the film to be wound back into the cartridge.
U.S. Pat. No. 4,717,931 discloses a fail-safe film prewinder for a camera. The prewinder has a mode switch which can be changed over by switching to a photographing mode upon completion of a prewinding mode in which a film is continuously pulled or prewound from a film cartridge loaded in the camera. When the mode switch is in the prewinding mode position while a shutter release button is being operated, a film transport motor is rotated in the direction to prewind the film again after an interruption of the prewinding mode.